1. Field of the Invention
The present invention relates to a light deflector, and more particularly to a planar electro-optical light deflector for controlling a light beam with respect to a plurality of beam positions.
2. Description of the Prior Art
Light deflectors for several beam positions are employed, for example, in the case of laser printers, because several vertically-superimposed points can be simultaneously recorded, as a consequence of which the number of recorded symbols, given the same horizontal recording speed, is multiplied.
It is known to employ ultrasonic deflectors for this purpose which are excited with several different frequencies, and each frequency then corresponds to a specific deflection angle (Schmidt, R. V.; Kaminow, I.P.; Carruthers, J. R.: Acousto-optic diffraction of guided optical waves in LiNbO.sub.3, Applied Physics Letters 23 (1973), p. 417). However, ultrasonic deflectors have the disadvantage that they require a (high) carrier frequency and a considerable amount of driving power.
Electro-optical light deflectors embodied in a waveguide exhibit considerable advantages with respect to their activation (or control) as compared with acousto-optical deflectors. Electro-optical light deflectors operate in the baseband; i.e. they are directly driven with the modulation frequency. Also, with regard to the driving power, the advantages clearly lie on the side of the electro-optical deflector, since a comparatively high high-frequency power is required for the generation of the sonic field in the acousto-optic deflector.
However, the known electro-optical Bragg deflectors in a waveguide embodiment make possible only two beam positions, which, moreovver, cannot be activated independently of one another (Hammer, J. M.; Phillips, W.: Low-loss single-mode optical waveguides and efficient high-speed modulators of the LiNb.sub.x Ta.sub.1-x O.sub.3 on LiTaO.sub.3, Applied Physics Letters 24 (1974), p. 545). The construction of a conventional electro-optical Bragg deflector in a waveguide embodiment is illustrated in FIG. 1. In an electro-optical crystal (e.g. LiNbO.sub.3, LiTaO.sub.3 or GaAs) an optical layer waveguide is produced. By way of an interdigital finger-shaped electrode structure, due to the electro-optical effect, it is possible to induce, through application of a voltage, a refractive index grid in a waveguide. If the light strikes the grid under the Bragg angle .theta..sub.B, it is then reflected and, thus, altogether deflected by the angle 2 .theta..sub.B, whereas, without voltage applied to the electrodes, it propagates (or travels) in straight lines. The Bragg angle in the crystal results from the grid constants .LAMBDA. and the light wavelength .lambda. in the crystal to EQU .theta..sub.B .apprxeq..lambda./2 .LAMBDA..
With known electro-optical prism deflectors in a waveguide embodiment (Tasi, C.S.; Saunier, P.: Ultrafast guided-light beam deflection/switching and modulation using simulated electro-optic prism structures in LiNbO.sub.3 waveguides, Applied Physics Letters 27 (1975), p. 248), more than two beam positions can, indeed, be obtained; however, these are likewise not capable of being activated independently of one another, and the light cannot be deflected, as desired, simultaneously in several directions.